Mangrove facts, figures and information for those attending the Coochiemudlo Mangrove Festival on 31st July.
The Mangrove Festival offers two self-guide walks through the island’s mangrove forest along its western shore. The North-western walk (#1) must be completed before noon as the tide will cover the track after that. The South-western walk (#2) is open all day. Both walks include most of the island species and habitat. You’ll be met at the jetty by Heritage Society volunteers to help you plan your day to include the things you most want to do.
Here’s some mangrove information that will help you get the most out of the walks by knowing a little about these amazing plants before you start. You can always keep this page on your mobile during the day as a reference to what you’ll be seeing.
Mangroves are survivors. They thrive in the hottest, muddiest salty conditions that would quickly kill most plants. Yet they also flourish in cooler waters like those in costal Victoria. They’ve evolved amazing adaptations, like their filtration systems to block and excrete the salt in their water uptake. Their weird and wonderful root arrangements that allow them to hang on and stay upright in the mud through wild storms and swirling tides. Their roots often rise above ground so the mangrove can breathe, as mud is severely lacking in oxygen.
Mangroves propogate by growing live ‘baby’ mangroves, called propagules, that form around their fruit and eventually fall to the foot of the tree. They're picked up by the tide and washed out into open water, where they can survive for weeks, even months. A tiny number settle in a suitable place long enough to take root and survive.
Mangrove forests absorb and store carbon from the atmosphere. They use it as the building blocks for their leaves, roots and branches. These eventually fall to the seafloor and take the stored carbon with them to be buried in the soil. This “blue carbon” reduces the harmful levels of carbon building in the earth’s atmosphere. It’s likely the Coochiemudlo mangrove forest stores about 60,000 kilograms of carbon a year. That’s equivalent to the carbon produced by 50 cars, in a year, each driving an average of 20,000 kilometres.
Coochiemudlo has seven of the eight mangrove species in Moreton Bay. They are, starting with the most common:
Grey mangrove Avicennia Marina. Up to 25m tall, area around the tree covered in short roots sticking up like fingers, underside of leaves is grey-green. Grows throughout the intertidal zone.
Stilt or Red mangrove Rhizophora stylosa. Up to 10m tall, reddish bark, aerial prop roots shoot out from the trunk to the ground. Prefers the water’s edge, tolerates frequent and permanent inundation.
Orange mangrove Bruguiera Gymnorhiza: Rough bark, large leaves, very distinctive 'knee roots' poking above ground. Red flowers with pointed tips. Cigar shaped green propagules hang from the flowers.
Yellow mangrove Ceriops australis. Smaller tree to 5m tall. Prefers drier habitat around the high tide mark. Yellow leaves, thin pencil shaped propagules, thickly-massed buttress roots in deeper water.
River mangrove Aegiceras corniculatum Bushy small tree to 2m tall. Grows on mounds and banks near or above high tide. Excretes salt onto its leaves. Small white flowers.
Milky mangrove Excocaria agallocha. Can grow from 2m shrub to a tree to 15m. Leaves are often close to the ground. The trunk is fawn coloured and dotted with air pores. Milky sap exudes from broken leaves. It’s poisonous and can cause severe skin irritation and temporary blindness in contact with the eyes.
Mangrove fern Acrostichum speciosum. Not seen on either walk, but domestic plants on display at the Community Hall in pots.